1. Field of the Invention
This invention pertains to a book binding system including binder for strips for retaining and clamping a margin of apertured material such as a stack of hole punched paper sheets. In particular, the invention is directed to self-locking binding elements used to manually bind a sheaf of papers into a bound report or booklet without the use of any machinery or hand tools. More particularly, the invention is directed to improved binding elements using a first strip having binding post legs with locking teeth cooperating with a second strip having hinged latching pawls.
2. Material Information
Self-locking binding systems employing ratcheting latching teeth on hinged pawls and post legs are disclosed in U.S. Pat. Nos. 4,730,972; 4,743,048; 4,874,186 and 4,893,836 all assigned to Applicant's assignee. These inventions utilize frangible post leg designs in order to facilitate manual removal of the excess post length. While such a design eliminates the need for binding machines or hand tools, it also results in post legs inherently weaker in the direction in which they are designed to break when removing the excess post length(s). High forces transmitted to the binding device by the pages of the bound book when subjected to abuse may result in undesired internal fracture of some of the post legs. The prior art patents teach post leg orientations in which all posts (usually three or four) on a strip have the same alignment for a given bound book. This orientation facilitated the snapping-off of all the excess lengths of all the posts.
The above prior art is illustrated schematically in FIGS. 1 and 2 where a stack 10 of paper sheets 7 having a marginal longitudinal edge 11, marginal side edges 8, 9 on the stack top and bottom, and typically three (or four) equally spaced punch hole apertures 12 in the side edge margins 8, 9 are bound by a first strip 14 having a corresponding number of upstanding integral bifurcated posts 15, 16 and 17 with facing ratchets. The apertured sheets stack is placed over the posts so that the ends 18 of the dual legs forming the posts extend from the paper stack. A second strip 19 includes a corresponding series of depending pawls 20 with pairs of D-shaped through-apertures 21 therearound through which the corresponding D-shaped legs 15-17 pass. As seen in FIG. 2 after the pawls-to-ratchets connection has been made the excess lengths of all the legs are snapped off at the top surface of strip 19. This causes some remaining exposed leg end surface roughness. A remaining post ratchet interacts with a corresponding pawl to fairly rigidly bind the stack marginal edges together to form a bound booklet.